There are a few other words with skipped syllables that are a bit more unusual:

comfortable – In this word the 2nd vowel is skipped, and the “A” is also skipped, plus the “rt” is reversed and pronounced as “ter”. So this ends up sounding like “comfterble”. There are some native speakers who are careful with this word and articulate the written order of the letters – “comfortable” – but the sound of the 2nd “O” is still lost because it is hidden by the R-vowel.

probably – In this word the 2nd vowel is often skipped, leaving a sequence of two “B” letters, which become a single “B” sound. However, this word is spoken both ways. It tends to be reduced to 2 syllables in more informal situations, but retains 3 syllables in more formal, careful, or emphatic speech.

Wednesday – This is the most unusual of all the words with a skipped syllable. The 2nd vowel is skipped, but the “D” of the 1st syllable is also skipped, so it sounds like “Wensday”. It is very rare to hear a native speaker pronounce it fully like it is spelled – which is usually only done to be humorous.

Is it necessary to skip syllables?

YES, only for “business” “Wednesday” “evening” & “vegetable”. These words sound strange without a skipped syllable.

NO, not necessarily, for the other words. Even though native speakers tend to skip a syllable, these words can be said without skipping a syllable. If you say all of the syllables, it makes them sound less smooth, but you would still be understood. However, you should be aware of them, to help you listen and understand English more easily.

A funny example.
My 4-year old son made a very funny mistake with a word that has a missing syllable: “asteroids”.

The word “asteroids” can be said as 3 syllables [ as ~ ter ~ oids ], but the “E” is hidden by the R-vowel. This easily changes to 2 syllables because the middle syllable “ter” shifts to combine with the last syllable, making [ as ~ troids ].

My son had heard the word “asteroids” in Star Wars but he did not know what it meant. He had also heard the term “Battle Droids” in Star Wars and he could see that this was a kind of warrior. So, one day I heard him playing an imaginary game of “Battle Droids” vs. “Ass Droids”.

You see, when “asteroids” is said as 2 syllables, it really sounds like “ass-droids”. Most adults probably never notice this, but since my young son did not know the meaning of “asteroids” he assumed it was the name of another kind of warrior. It turns out that he did not know the meaning of the word “ass” either!